


On Theoretical Physics and Cohabitation

by orphan_account



Category: Supergirl (TV 2015)
Genre: Established Relationship, F/F, Moving In Together, SuperCorp, SuperCorp Week, Time Travel, Time Travelling Lesbians
Language: English
Status: Completed
Published: 2017-12-24
Updated: 2017-12-24
Packaged: 2019-02-20 05:50:29
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,921
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13140390
Author URL: https://archiveofourown.org/users/orphan_account/pseuds/orphan_account
Summary: Like most lesbians, all Lena really wants is a live-in girlfriend and a cat.  Unlike most lesbians, Lena has to convince her girlfriend that that their future selves traveled into the past to help her figure out that it's about damn time that they move in together.





	On Theoretical Physics and Cohabitation

**Author's Note:**

> Written for Day 6 of SuperCorp Week. Prompt: Time Travel.

“Do you think we’re in a fixed timeline, a dynamic timeline, or a multiverse?” Lena asks.

They’re in her bed watching TV, piled under every blanket Lena owns and surrounded by at least a dozen different snacks, when Lena finally figures out how she’s going to convince Kara to move in with her, and maybe also get a cat. 

She’s wanted Kara to move in for a while now. They love each other and Lena is sick of going to bed and waking up alone. But Kara doesn’t seem to want to move in. Lena tried asking nicely, but Kara said she wasn’t ready. So Lena waited. Eventually, Lena tried asking rudely, but Kara had stupid excuses. So now Lena has more blankets and snack foods lying around than she knows what to do with, but no live in girlfriend. 

Really it’s Kara’s fault that she’s resorting to trickery because Kara’s left her no other choices. And Alex may have mentioned that sometimes Kara needs a not-so-gentle shove in the right direction. 

“Explain please.” Kara pauses the television. She knows they live in a multiverse, but she hasn’t explained that much to Lena just yet. She only told Lena she was an alien a few months ago and they’ve only been officially dating for a few months. She doesn’t want to freak Lena out by dropping too much otherworldly knowledge on her at once. 

“In a fixed timeline, you can’t actually change the future. The thing you’ve gone back to prevent was probably caused by whatever you did when you went back. Your fate is sealed.” Lena begins. 

“And in a dynamic timeline?” Kara asks.

“In a dynamic timeline, you can change the future, but you can also find yourself in a time loop. You go back, kill your mom, you’re never born, but then no one goes back to kill your mom. So then you’re born, you grow up, and you go back to kill your mom, and so on forever.” Lena explains. 

“And in a multiverse?” Kara asks. 

“Every time you go back, you create a new timeline where you can change the future, but you cant ever go back or change your original timeline. So there could be an infinite number of parallel timelines.” Lena finishes. 

Kara pauses for a moment. She can practically see the wheels turning in her girlfriend’s head, but she can’t suss out where Lena’s mind is going. Kara knows not to underestimate Lena though, so she decides to go with the truth. 

“We’re clearly in a multiverse.” Kara announces. 

Lena notices the authority in Kara’s tone and is momentarily taken aback. She sometimes forgets that there’s a whole other world of knowledge in Kara’s head. Her plan to get one or two new housemates suddenly pales in comparison to the possibility of actually figuring out time travel. But surely if Kara knew about the science behind time travel she would have gone back and changed the fate of her planet, Lena reasons. She wonders if perhaps Kara is just much more into the show than she’d realized. 

“Do you mean us or the TV show?” Lena asks. Kara chuckles. They’re binge watching Continuum - Lena had wanted sci-fi, Kara had wanted a strong female lead, and Netflix had provided for them both. 

“I mean us.” Kara squeezes Lena’s hand. “Do you remember my friend Barry? He’s from a parallel universe.” 

“Holy shit.” Lena sputters. 

“Well, it’s not exactly the same.” Kara muses.

“Isn’t that the point?” Lena asks.

“No, I mean it’s not exactly the same as the time travel theory.” Kara clarifies. “We can move from one timeline to another, but we can also go back to our original timeline. And you can’t do that in the multiverse theory. You’d be in a new timeline.” 

“Have you been to other universes? How do you know this isn’t a new timeline and there’s a poor sad Lena in your last one just waiting for you to come back.” Lena begins gesticulating wildly. “Oh god, that Lena can’t be in a good place. She’s probably going to take over the world.” 

Kara laughs, she can’t help it. “It’s not time travel, its just universe travel.” She explains.

“JUST UNIVERSE TRAVEL.” An exasperated Lena parrots back. “And you never said anything to me about it?”

“I can’t exactly do it on my own.” Kara pouts. “We’re getting off track.” She does not want to find herself going down the road of all the things she’s yet to tell Lena. 

“I want to travel between universes.” Lena whines. 

“You don’t even like flying.” Kara teases. 

“But I do it.” Lena points out.

“My brave little Luthor.” Kara kisses her cheek. Surprisingly, Lena doesn’t swat her away after making a comment like that. But Lena is clearly lost in her own head.

Kara waits her out. 

“So we live in a multiverse.” Lena finally sighs. 

“Sort of.” Kara reminds her. “As in we do, but not necessarily in the time travel theory version of a multiverse because as far as I know, no one has figured out time travel yet.”

“So we live in one of many parallel universes, but each one could be fixed, dynamic, or part of a multiverse of its own.” Lena surmises. 

“Correct.” Kara nods. 

“So we haven’t really even gotten to my original question yet.” Lena says. The hair on her arms is sticking straight up and she’s covered in goose bumps.

“Want to watch Friends?” Kara rubs her arm soothingly.

“I’m not switching shows two and a half seasons in unless you find me something with actual queer representation.” Lena crosses her arms over her chest. 

“Good. I’m really into this show and I want to see what kind of timeline they live in.” Kara smiles. “Are you okay?”

“Yeah.” Lena nods. Her mind is blown, but her subconscious will have this conversation processed soon enough and then she can figure out what to do with the information. 

“I love you, you know.” Kara snuggles herself closer to Lena. 

“I know.” Lena adjusts herself into proper little spoon form and takes in a deep breath. She needs to get herself back on track. 

“And you love me too.” Kara prods.

“I do.” Lena grins. “And I’m going to figure out time travel.” 

______________________________

Four days after they finish Continuum, Kara flies in on Lena furiously working out a formula on a giant whiteboard in her kitchen. 

“I’m not loving the new decor.” Kara jokes while placing a box of fresh chocolate filled croissants on the kitchen island. 

“Well, if you lived here you could have a say in the decor.” Lena answers without turning away from the board. 

“I brought breakfast fresh from that French place you love.” Kara thanks Rao she brought treats because she does not want to have this talk with Lena right now. So instead of telling Lena that she’s not moving anytime soon, she wraps her arms around Lena’s waist from behind and decides she can distract her with food. 

Lena pries her attention from the board and finally looks at Kara. “I haven’t found any French places I like here yet.” 

“I know, which is why I flew to Montreal.” Kara smirks. She absolutely loves how Lena - who finds herself in Europe at least five times a year for L-Corp business - thinks the best French food is in Canada. 

“You make me so happy.” Lena kisses her. 

“And it didn’t even take a cat.” Kara jibes. 

“I didn’t say I couldn’t be happier.” Lena grumbles through a mouthful of croissant. 

______________________________

Kara begins to worry about Lena when a full week goes by without Lena asking her to move in or adopt a cat. To be fair, they’ve spend maybe three waking hours together in total with all the extra time Lena’s been putting in at L-Corp. 

Kara really hopes Lena’s crazy work schedule isn’t all because of their conversation about time travel or the multiverse, but she’s pretty sure it is based on the now three whiteboards covered in equations and messy scribbles that have taken over Lena’s kitchen. 

She’s on her way to talk to Lena about it. It’s ten at night and she’s apprehended two aliens and turned in an article edited so well that Snapper can’t possibly have anything mean to say. 

She can hear Lena’s heart beat coming from L-Corp and she decides its time to break Lena out of work and force her into doing something fun and relaxing.

But her com buzzes.

“We need Supergirl.” Alex’s tired voice rings in her ear. 

______________________________

Lena almost feels guilty about how much time she’s been spending at work. But L Corp is about to unveil a new method of creating vaccinations that she’s pretty sure will change the world. 

And she doesn’t mind in the least that Kara thinks she’s working on figuring out time travel. Lena wouldn’t have bothered to fill her kitchen with giant white boards filled with nonsensical gibberish and random equations had she known she’d basically be living at work this week. 

Ironically, today she’s going to have to stay late to finish all the work she can’t seem to do because all she is thinking about is time travel. Not so much the science - as much as she loves theoretical physics, she’s a bioengineer and a businesswoman - but what it would look like. She’s been trying to figure out how a time-traveler would appear in a new timeline. Would there be smoke? Flashing lights? Would they stumble? If her plan is going to work, it’s got to look real. 

Her phone rings and she loses her train of thought. “Miss Danvers is here to see you.” Jess reports. 

“Thanks, Jess. You can add Alex to the list too.” Lena tells her. 

“Will do, Miss Luthor.” Jess responds. Lena hangs up just as the door swings open. 

Alex is wearing an FBI jacket and radiating stress. Lena hides her panic. Alex’s visits aren’t rare, but they’re certainly not common. And Alex always calls first if it’s a casual visit. So Lena assumes something is wrong. Either Kara is hurt or there’s a Luthor problem. 

“What’s wrong?” Lena tries to keep her tone casual. Alex’s face is pale and the circles under eyes are as dark as Lena’s ever seen them. 

“She wants to tell you everything, Lena.” Alex sits in front of Lena’s desk. “You have to make your move now.” 

Lena breathes a sigh of relief. It genuinely hadn’t occurred to her that Alex’s exhaustion might have nothing to do with her. “Everything?”

“About the DEO, her team, everything.” Alex rubs her eyes. “God only knows how she hasn’t realized that you figured the DEO out long before you knew she was Supergirl.”

“I mean obviously Supergirl has a team, and obviously it’s the people that seem to show up at every one of her fights.” Lena smirks. She gets up to pour Alex a drink. 

Alex spins around in her chair to watch her. “And yet you couldn’t see past the outfit and the glasses.”

“I know.” Lena shrugs. She brings Alex a glass of water and a glass of her favorite scotch. “Are you okay?”

“I’m too old to be pulling all nighters.” Alex takes a few sips of the water. “Criminals need to keep better hours.” She moves onto the scotch. 

“Why don’t you let my driver take you home?” Lena suggests. 

“I have to go back to work, actually.” Alex finishes the scotch. Lena nods in understanding. “But I came here because this is the literal perfect time to execute the plan.” 

“And L-Corp is across the street from your favorite coffee shop.” Lena snorts.

“That too.” Alex grins. “So I’ll send J’onn and M’yrnn over around 7?”

“Yeah.” Lena figures her actual work will have to wait. “I still haven’t figured out their entrance, or what they should say.”

“We’ve got the dialogue covered.” Alex says. “J’onn has known Kara for a lot longer than she realizes. My mom had some ideas about what might be holding her back too.”

“You told Eliza?” Lena is shocked.

“Of course.” Alex laughs. “It takes a village to hoodwink an alien.”

“As the proverb goes.” Lena laughs. 

“So let’s work on the entrance. How does Kara usually come in?” Alex asks.

“The balcony.” Lena answers.

“And how would you prefer she come in?” Alex asks.

“I mean, the door is how one should enter, but if I’m being honest, I like the occasional surprise visit.” Lena thinks aloud. “And when she comes over late, I love that I don’t have to get out of bed to answer the door.” 

“Now, if she were to say come around seven on a day you definitely weren’t expecting her and probably had other plans?” Alex continues. 

“I’d prefer a knock.” Lena supplies, thankful for Alex’s calm practicality. 

“Good. Then they’ll knock. They’re pretending to be you two, they will do what you two would do.” Alex shrugs. “Would do? Will do?” 

“Just stop yourself there.” Lena laughs. “I’ve lost a lot of time thinking way too hard about it.” 

“I’ll bet.” Alex grins. “It’s about time my sister moves in with you. You have a much nicer entertainment system.” 

“And I’m closer to everyone’s favorite pot sticker place.” Lena adds.

“In all seriousness, Lena. She loves you. She spends half her free time worrying about you, and the other half she spends with you.” Alex says. “I don’t know why she’s been so hesitant about moving in with you, but I think this is just the push she needs.” 

“Thanks, Alex.” Lena says.

Alex’s phone buzzes. She looks down at it and groans. “Kara is a terrible patient. I have to get back to the DEO.” 

“Patient?” Lena jumps up. So Kara is hurt. 

“Oh, sorry.” Alex stands. She leans against the chair and laughs sheepishly. “She’s okay. She solar-flared, basically burnt out her powers during her all night fight.”

“So, she’s human?” Lena asks.

“I mean she’s still an alien.” Alex shrugs. “But, basically, yeah.”

“So she wont be able to hear my heart beat or recognize that our time-travelers don’t smell like us or whatever else she can do?” Lena asks. This seems too perfect.

“Exactly.” Alex smiles, the stress of her night appears to be slowly fading. 

______________________________

Lena spends the rest of her day scanning through paperwork and counting down the minutes until she gets to see Kara. Kara spends the rest of her day under a sun lamp.

At a quarter till seven, Kara knocks on Lena’s apartment door. She’s wearing comfortable clothes and carrying a much lighter bag of Chinese food than usual. 

“Alex told me you solar flared.” Lena says, giving Kara a warm hug.

“At least it means I have the weekend off.” Kara says. “We can start a new show!”

Lena’s phone buzzes moments before there’s a knock on the door. 

“Can you get that, babe? I have to take this.” Lena lies. Kara nods, and Lena gives her a quick kiss on the cheek before disappearing into her study. 

Kara slips her glasses down her nose before remembering that she’s without her powers. She pushes them back up and opens the door. 

“Hi, how can I –” Kara stops in her tracks. 

She’s eye to eye with Supergirl – or, well, herself – and Lena. Supergirl has a sheepish grin on her face and Lena is straight up smirking. 

Kara panics and slams the door shut. She races around the corner and down the hallway towards Lena’s study. Lena spots her and puts her hand over the speaker.

“I’ll just be another minute, babe.” Lena says.

“Yeah,” Kara nods, not wanting to alarm her. 

She runs back into the kitchen. Her visitors are sitting at Lena’s table. 

“There’s no need to be alarmed, dear.” The new Lena says, slipping a key back into her handbag. “We’ll keep our visit brief.” 

“Who are you?” Kara asks.

“You know who I am, Kara.” Lena raises an eyebrow. “I told you I would figure out time travel, didn’t I?” 

“You’re not usually one to gloat.” Kara crosses her arms.

“She freaking figured out time travel!” Supergirl says, squeezing future Lena’s hand. “I may have told her we didn’t actually believe that she’d be able to figure it out.” 

“Oh Rao.” Kara takes a seat at the table. She looks at the future version of herself and her girlfriend for a few silent moments. She has no idea what to say because holy freaking Rao Lena figured out time travel. 

“If you’ll excuse me, I need to have a chat with myself.” Future Lena excuses herself.

She watches her future self watch future Lena walk out of the room. 

“We also need to talk.” Supergirl leans towards her. 

“Can we save Krypton?” Kara asks. 

“Our Krypton is gone.” Supergirl takes her hands. “There is nothing you can do or could have done that would have changed what happened.” 

Kara’s eyes water in relief. Sure, she’s heard that a thousand times, but this is the first time she’s believed it. “Okay.”

“We’ve lost a lot, Kara.” Supergirl says. “But it’s never been your fault. You are so happy right now; you feel like you’re on the brink of having another real home, here with Lena.” 

Kara knows she shouldn’t be as shocked as she is that a future version her understands exactly how she feels, but she can’t help it. She’s speechless. 

“You’re not on the brink though, Kara. You’ve found a home with Lena, whether or not you make it official – move in, propose, start a family – whatever that means to you today.” Supergirl continues. 

“I can’t.” Kara shakes her head. 

“I get it, Kara. Your home on Krypton was taken from you. Your chance to raise your cousin was taken from you. Jeremiah was taken from you. Just because you’ve found a home here, doesn’t mean it’s going to be taken from you.” Supergirl says. 

“Doesn’t it though?” Kara responds. 

“I wish I could lie to you and say I was from a very distant future, but I’m not. Trouble often follows you both and I don’t know what will happen, but I do know that pretending like you haven’t found a home here isn’t going to keep you from losing her.” 

“I would have preferred you lie to me.” Kara swallows back the urge to cry. 

“You would have seen through it.” Supergirl smiles softly. “You can’t let your fear hold you back. We’re braver than that.”

“Can you just tell me that everything is going to be okay?” Kara sighs. 

“Look around.” Supergirl stands up. She points to the photo on the fridge – a selfie Kara took of Lena kissing her cheek in front of the Supergirl statue – and she puts her hand over Kara’s heart. “Everything is so much more than okay.” 

Kara looks around. She sees the piles of blankets on the couch, her favorite kind of chips on the counter, and it dawns on her that Supergirl is right. 

“Thank you.” Kara says. “I needed this.”

“I know.” Supergirl nods.

“Sorry dear, but we’re going to be late.” Future Lena interrupts them. She squeezes Lena’s shoulder before meeting Supergirl and Kara by the door. 

“Look sweetheart, I’m using the door.” Supergirl jokes, holding the door open for future Lena. 

“Good bye, you two.” Future Lena gives them a smile before pulling the door behind them. Kara pushes her ear to the door and watches them from the peephole. 

“I’m gad we did that.” She hears future Lena say. 

“Me too, but we’re going to be late. Len must be starving!” Supergirl replies. Supergirl takes future Lena’s hand and glances at the door one last time. 

To Kara’s surprise, she brings her face right up to the peephole. “Stop eavesdropping.” Supergirl shakes her head. Then she and future Lena move down the hallway and towards the elevators. 

Kara turns around and sees Lena pouring two glasses of wine. 

“That was … unexpected.” Kara says, taking one of the glasses. She’s actually grateful she’ll be able to feel its effects tonight. 

Lena notices Kara’s red eyes, and her smile drops instantly. She panics that her gentle shove was maybe a stab in the back. “Babe, I’m so sorry.”

“No, Lena, no.” Kara stops her. “These are happy tears. Future me knew exactly what I needed to hear.” 

“So everything is okay?” Lena asks.

“Everything is so much more than okay.” Kara smiles. She pulls Lena in for a kiss. She takes in the softness of her lips, the warmth of her mouth, the way that Lena’s body feels pressed up against hers. 

When they finally part, Kara presses her forehead against Lena’s. “I’m ready to move in, Lena. I want to make this our home.” 

Lena pulls her in closer. “I couldn’t be happier.” 

______________________________

Kara spends the next few days basking in the happiness that is living with the love of her life. It isn’t until Supergirl saves an infant that she remembers what she overheard. 

Future Supergirl looked just like her, but Kara doesn’t age very fast. And she hadn’t spent enough time with Lena to suss out how close of a future they were from. 

But now it’s all she can think about. Because, yes, she was ready to move in with her girlfriend, but she is by no means ready for a child. So even though it isn’t even noon yet and Kara has a stack of work waiting for her at Catco, she flies right to Lena’s balcony.

Jess, who is bringing Lena a mug of coffee and a stack of files, notices her first. She waves, which alerts Lena to her presence. 

Kara waves back at Jess, but doesn’t come in. Instead she waits on the balcony for Lena to come out.

“You have Jess worried.” Lena shakes her head at Kara.

“Sorry, I need to be at work, but I had an important question.” Kara says. 

“Okay.” Lena nods. 

“Lena, if we had a kid one day, would you want to give them an L name?” Kara asks. 

Lena gives her an incredulous look. 

“For real, I need to know.” Kara says. “It’s just something I overheard future me say.”

Lena nods. “Not particularly. You’ve lost a world of family, I think it would be nice to name any theoretical children after one of them.” Lena answers. Kara sighs in relief. It’s an animal then or they’re babysitting, or really there are thousands of possibilities. But they don’t have a child in the near future and that’s all Kara needed to know. 

“Will you be home in time for dinner tonight?” Kara asks. 

“Yes.” Lena laughs at the dramatic change in tone. 

______________________________

Kara’s relief is short lived though. When she gets back to the DEO she sees Alex, Winn, and J’onn standing with M’yrnn who is holding a box of kittens. 

Winn greets her with two kittens. “He’s basically the Supergirl of animal rights.” Winn coos to an orange and white tabby. He hands her the other kitten. A little black boy with white paws and a white strip down his back.

Kara is a dog person, first and foremost. But even she can admit that the kitten is cute. “What’s this little guys name?” She asks, walking towards the group. 

“J’onn named that one Lynyrd Skynyrd.” Alex rolls her eyes. 

“Shit.” Kara whispers. “I guess Lena and I have a cat now.”


End file.
